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Interference avoidance and mitigation to support overlaid CSG-closed femto ABS (16.4.11) Document Number: IEEE C80216m-09_2946 Date Submitted: 2009-12-30 Source: Ying Li, Baowei Ji, Zhouyue Pi, Email: yli2@sta.samsung.com Phone: +1-972-761-7903yli2@sta.samsung.com Youngkyu Baek, Jung Je Son, Anshuman Nigam, Young Bo Cho Samsung Electronics Venue:IEEE Session #65 Base Contributions: Re: Contribution in support of a comment on LB30b Purpose: Discussion and Approval Notice: This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the Source(s) field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

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Problem definition Large interference from an inaccessible Femtocell may saturate or block the MS radio receiver, such that it will not able to maintain the communication with the serving BS. When a non-member AMS is seriously interfered by a neighbor CSG-closed Femtocell ABS and cannot get any service from the network, what should be done for such MS?

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IM for macro and femto Femto and overlay macro at different FA – No IM issue – But, spectrum is expensive. – It may not be acceptable to buy an additional carrier frequency to support femto. Femto and overlay macro at same FA – For CSG-open and Open femto HO is a solution for IM Resource reservation can be done – For CSG-closed femto Valid use case But, possible coverage hole for non-member MSs Most difficult 3

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Macro and overlaid CSG-closed femto at same FA (1/2) If non-member MS is still connected to macro or any ABS, but sees strong interference from CSG-closed Use coordinated IM – MS measures the DL from CSG femto, report interference to the serving BS – If IM is needed, serving BS and interfering CSG femto will negotiate via backhaul, to mitigate the interference. Reserve resource time/frequency Power control – MS measures the DL from CSG femto, report interference, and terminate IM and release resource when interference is not needed. 4

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Macro and overlaid CSG-closed femto at same FA (2/2) If non-member MS is not connected to macro or any other ABS, and AMS can only see a CSG-closed femto Since MS can only see a CSG-closed femto, the remedy can be – Step 1: MS signals CSG-closed femto, to request IM – Step 2: FBS may notify the IM request to the macro and backhaul, to have coordinated IM, based on the operator or service rules. In such scenario, we need solution for IM on both control and data channel Staggered SFH makes MS scanning complicated. It is removed from AWD. We lose one degree of freedom. At Step 2, the remaining degrees of freedom can be – Frequency: FA change, if available – Power: power control – Service agreement: CSG-closed FBS exceptionally serve non- member with low priority [CSG-closed temporarily becomes a CSG- open virtually, without changing cell ID] The above can be used as femto and femto at same FA. 5

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Step 1: non-member signals CSG-closed femto If non-member MS is not connected to macro or any other ABS, and AMS can only see a CSG-closed femto MS can only see a CSG-closed femto, so the remedy can be (details in contribution #2596 or its latest version) – Trigger: a disconnected AMS who is a non-member of a CSG-closed femto measures that the CSG-closed femto ABS is the only ABS with a RSSI or CINR higher than the minimum acceptable RSSI or CINR for MS to access a BS, for a period of time T greater than a threshold TH1 – Action: the AMS may request the femto ABS to mitigate the interference by sending an AAI_RNG-REQ message with Ranging Purpose Indication Bit #7 set as 1. 6

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Step 1 - Solution (1/2) This case is for that an AMS has no valid AK context. If an AMS is seriously interfered by a neighbor CSG-closed femto ABS and cannot get any service from the network, the MS may request the femto ABS to mitigate the interference. MS can send an AAI_RNG-REQ message with Ranging Purpose Indication Bit#5 set as 1. Having received this IM indication, the CSG- closed Femto ABS may further allow MS to enter the EAP stage for authentication. If the FBS recognize the AMS is illegal, it rejects any request from MS. If the FBS recognize that the AMS is a legal user but a non-member, the FBS may either accept the IM request, or reject. Whether to accept the request of IM or reject, depends on the FBS service provider or operator rule. Advantage: – Prevent the CSG femto generating coverage hole to non-member MS Non-member AMSCSG-Closed FBS A-preamble SFH Initial ranging code RNG-RSP RNG-REQ, with a purpose bit indicating IM SBC-REQ/RSP PKM-REQ PKM-RSP Interference mitigation Receiving SFH, MS can judge whether it is a member/non- member of FBS based on CSGID/BSID Authentication

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Step 1: Solution (2/2) This case is for that an the case that an AMS has a valid AK context This can happen, for example, AMS was in idle state served by a macro BS, but now it cannot hear macro, but only a strong interference from inaccessible CSG-closed FBS. If an AMS is seriously interfered by a neighbor CSG-closed Femtocell ABS and cannot get any service from the network, the MS may request the femto ABS to mitigate the interference. MS can send an AAI_RNG-REQ message with Ranging Purpose Indication Bit#5 set as 1, and the CMAC is contained. The Femto ABS may authenticate the request. If the FBS recognize the AMS is illegal, it rejects any request from MS. If the FBS recognize that the AMS is a legal user but a non-member, the FBS may either accept the IM request, or reject. Whether to accept the request of IM or reject, depends on the FBS service provider or operator rule. Non-member AMSCSG-Closed FBS A-preamble SFH ranging code RNG-RSP RNG-REQ, with a purpose bit indicating IM. RNG-REQ contains CMAC RNG-RSP Interference mitigation Receiving SFH, MS can judge whether it is a member/non- member of FBS based on CSGID/BSID Authenticati on

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Step 2: Policy 2- power control Femto and macro have coordinated IM – Femto will reduce its transmission power for DL control channels. If femto power is reduced to an extent that all the MSs being served are handed out, femto can enter LDM. Pros: CSG-closed does not really serve non- member along data traffic. Cons: Member MS of CSG-closed may be hurt/affected (e.g., may be handed out) 10

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Step 2: Policy 3- Temporary CSG-closed to a virtual CSG-open (only as an example of one of the possibilities) Femto CSG-closed may be temporarily a virtual CSG-open, and this is triggered by the event. CSG-closed may not need to change the cell type by changing cell ID (pick a cell ID from the partition for CSG-open). – If such IM request occurs not frequently, dynamic temporary virtual change (no cell ID change) can be a good fit. Such virtual change should not cause the NBR-ADV update. – Optionally, of course, it could change the type from CSG-closed to CSG-open, starting from changing cell ID. The non-member could get the service in a low priority if there is resource available. The cell is still a CSG-closed in regular mode. It will be open only when such IM request occurs. It is different from CSG-open which is open all the time. Pros: Member MS of CSG-closed is not hurt/affected. Cons: CSG-closed now serves non-member. 11

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Step 2: Policy 4- Rejection Possible rejections – Femto detects #7 purpose bit in RNG-REQ for IM request, and femto reject such ranging, without going further to authentication. [Should provide a response to MS, tell MS it is not allowed by the policy and not to try again] – Femto detects #7 purpose bit in RNG-REQ for IM request, and femto goes further to authentication. If the authentication result is that MS is an illegal user, reject. If MS is a legal user and non-member, and if the policy does not allow IM for this particular user (there could be a policy that only some users or partners who can enjoy the IM). [Should provide response to MS, IM not allowed] If MS is a legal user and non-member, and if the policy allows power control to do IM, but power control fails, reject. If the policy allows CSG-closed temporarily to be a CSG-open, but there is no resource remaining, reject. [Should provide a response to MS: IM allowed but failed] 12

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Low duty mode It does not solve the problem of IM for overlaid femto and other BSs at same FA, because in AI, it still interferes other BSs. However, it can help downlink control interference mitigation. For example, with LDM, the scenario that a non-member MS could not hear macro BS will occur with much smaller probability. Once non-member could communicate with macro BS, non-member could report interference from CSG-closed femto in LDM, even during NE stage, and macro could ask femto in LDM to perform power control to reduce the interference of DL control. Hence, it is beneficial to support LDM. 13

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Proposed text (1/2) Insert the following text to page 604, line 49 If an AMS is severely interfered by a neighbor CSG-closed femto ABS and cannot get any service from the network, the MS may request the femto ABS to mitigate the interference by sending an AAI_RNG-REQ message with Indicator of coverage hole due to inaccessible femtoset to 1, to indicate the interference mitigation request. If the AMS has a valid AK context, the AAI_RNG-REQ message shall contain CMAC tuple. Upon receiving Indicator of coverage hole due to inaccessible femtobeing 1, if the femto ABS does not accept this type of ranging request, it rejects this request. If the femto ABS accepts this type of ranging request, the femto ABS and the network may further authenticate the AMS. Only if the non- member AMS is authenticated, the femto ABS should accept the request.

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Proposed text (2/2) On page 46, 16.2.3.1 AAI_RNG-REQ In Table 674, insert the following item 15 NameValueUsage Indicator of coverage hole due to inaccessible femto 1: it indicates that an non-member AMS requests interference mitigation to a CSG-closed femto ABS, to compensate for the coverage hole generated by the CSG-closed femto 0: it indicates that it is a regular AAI- RNG-REQ Indicates that an non- member AMS requests interference mitigation to a CSG-closed femto ABS, to compensate for the coverage hole generated by the CSG- closed femto